The protective role of mannose-sensitive fimbriae in mouse typhoid

Abstract

This study was performed to determine whether type-l fimbriae of Salmonella were protective antigens in mice. We used a strain of S. typhimurium F885 which causes strong haemagglutination of guinea pig erythrocytes (haemagglutinating power = 3,200), which was inhibited by D-mannose, and methyl α -D-mannopyranoside. Mannose-sensitive fimbriae were released from these bacteria by high speed blending and after the method of Dodd and Eisenstein, the fimbriae were resuspended in 5 M urea to disaggregate cell membranes and flagella, leaving the urea-resistant fimbriae intact to be further purified by ultra. centrifugation. This method was found to give higher yields than two other methods, namely that of Salit and Gotschlich, and Knut ton et al. The fimbriae were found to be pure by immunoelectrophoresis criteria and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with an apparent subunit molecular weight of 19,000; they gave strong haemagglutination with guinea pig erythrocytes. Examined by electron microscopy, the diameters were 6 nm and retained their native morphology in the purification process. Protective studies were carried out in groups of mice which were vaccinated orally with 1x10 10 whole cells of S. typhimurium F885 of E.coli F492. or with 50 µg of fimbriae injected intraperitonealy on day 0 and subcutaneously on day 12. All groups of mice were subjected to oral challenge with 1,000 LD50 of the virulent strain, S. typhimuri um Cs. The percentage of deaths, and the numbers of challenge organisms in the spleen and Peyer's patches were significantly less in the S. typhimurium F885 and fimbriae immunized mice than in those of controls and E.coli F492 immunized mice. Further, there appeared to be a correlation between the protective ability of these strains and their ability to persist in the small intestinal Peyer's patches. Lipopolysaccharide (LPS) seem to plays no part in the bacterial protection, because the protective strain F885, and the challenge strain C5 carry quite different O-antigens. These results are consistant with the hypothesis that type-l fimbriae of strain C5 act as virulence factors by facilitating adhesion to intestinal epithelia and provides another example that purified fimbriae can serve as safe and effective vaccines.